Process for producing an electrographics roller

ABSTRACT

A roller is equipped with an elastic layer comprising a foam, wherein at least a part of the elastic layer is subjected to permanent compressional deformation by heating compression, and the cells in the elastic layer subjected to permanent compressional deformation by heating compression outnumber the cells therein before the heating compression; and a process for producing the above roller in high efficiency. The above process enables the production of the roller in which the surface state of only an arbitrary portion thereof is modified according to the purpose of use, and the roller thus obtained can exhibit high performances in a variety of applications including paper feed roller, developer conveying roller and so forth.

This is a division of Ser. No. 08/899,648 filed Jul. 24, 1997, now U.S.Pat. No. 5,893,821.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a roller and a process for producingthe same. More particularly, it pertains to a roller such as a developerconveying roller (also referred to as "developer feed roller"),electrifying roller, transfer roller, developing roller, cleaning rollerand paper feed roller each to be used in an electrophotographicapparatus or electrostatic recording apparatus such as a copying machineand printer; and to a process for producing said roller.

2. Description of Related Arts

An electrophotography recording apparatus which is widely utilized for acopying machine, a laser beam printer and the like is equipped generallywith a photosensitive body in the form of a drum (herenafter referred toas "photosensitive drum") and functions so as to form an electrostaticlatent image by carrying out electrification and exposure against saidphotosensitive drum; then allow a developer such as a toner (hereinaftersometimes referred to as "toner") to adhere to the photosensitive drumin accordance with the latent image on the drum to proceed withdevelopment; subsequently transfer the toner on the drum to a recordingmedium such as a recording sheet for the purpose of image transfer;thereafter electrically discharge the drum to a prescribed potential andclean the toner remaining on the drum; and then prepare the recording.The toner carried on the recording medium by means of image transfer isfixed onto the recording medium by being molten and pressure stuck, thuscompleting a series of recording work.

In the following, simple description will be given of the conveyance ofthe developer in the aforesaid series of recording work. Specifically,for example, a developer which is filled in a developing apparatus isfed to the surfaces of a developing roller by means of a developerconveying roller (developer feed roller) and is regulated to a uniformthin layer by a blade. While the developing roller is rotated in contactwith or in close proximity to a photosensitive drum under theabove-mentioned developer condition, the developer is stuck to theelectrostatic latent image on the drum from the developing roller tovisualize said latent image.

With recent progress of electrophotographical technique, a variety ofrequisite characteristics come to be imposed upon a roller such as adeveloper conveying roller, electrifying roller, transfer roller,developing roller, cleaning roller and paper feed roller each being usedin an electrophotography recording apparatus. One of the aforesaidrequisite characteristics is that an alteration be made in the surfaceconditions of only an arbitrary part of a roller.

The reason for such requisite characteristics being demanded variesdepending upon the type of a roller as described hereunder. In the caseof an electrifying roller, transfer roller, developing roller andcleaning roller, there have been a problem in which since the roller isrotated in contact with a photosensitive drum, the frictional forcebetween the roller and the drum, when being excessively strong, resultsin a large-sized electric motor for driving the roller, the need forreplacing the existing electric power source with a power source havinga larger capacity.

On the other hand, in the case of a paper feed roller, whose generalstructural drawing is given in FIG. 3, a shaft 21 is equipped with ringbodies 22 made of a synthetic resin, over which are fitted rubberyelastic layers 23. Such a paper feed roller in which a shaft 21 isequipped in advance, with a plurality of elastic layers 23 is directedto the prevention of meandering of a recording medium which feeds sheetsof paper. However, a paper feed roller of such a structure has involvedthe problems of intricate and large number of production steps andconsequent high production cost.

In addition, the developer conveying roller is called upon (1) to makean elastic layer low in hardness, smoothen its surface, secure a nipbetween the developer conveying roller and the developing roller andensure a sufficient amount of a developer to be conveyed; (2) to enhancethe density of cells on and around the surface of the developerconveying roller so as to prevent the surface thereof from being cloggedwith the developer; and (3) to eliminate scuffing on the surface of thedeveloper conveying roller and prevent foreign matters such as a foamand cellular material from mixing in a developing apparatus.

Under such circumstances, various methods have been developed for thepurpose of producing a developer conveying roller which satisfies therequisite characteristics in the preceding items (1) through (3). Theabove-developed methods, however, have both advantages anddisadvantages, thus failing to readily produce a developer conveyingroller which simultaneously satisfies all the aforestated requisitecharacteristics.

SUMMARY OF THE INVENTION

In such circumstances, intensive research and investigation were made bythe present inventors on a roller and a process for procuing the sameinvolving such problems. As a result, it has been found that a roller isreadily improved in its surface state at a low cost by heatingcompressing a part of an elastic layer comprising a foam for a rollerhaving said elastic layer, and in particular, that the number of cellsin a part of the elastic layer can be made more than the number thereofprior to the heating compression. The present invention has beenaccomplished by the foregoing finding and information.

It is an object of the invention to provide a roller whose surfacecondition of only an arbitrary part is altered in an inexpensive andsimple manner.

It is another object of the invention to provide a smooth andscuffing-free roller having an elastic layer of low hardness and of ahigh density of cells on the surface.

The first aspect of the present invention relates to a roller equippedwith an elastic layer compriseing a foam, at least a part of saidelastic layer being subjected to permanent compressional deformation byheating compression. It is desirable in this case, that the cells in theelastic layer subjected to permanent compressional deformation be madeto outnumber the cells in said elastic layer prior to the heatingcompression. It is desirable as the case may be, that a skin be formedon the surface of the elastic layer.

The second aspect of the present invention is concerned with a processfor producing a roller equipped with an elastic layer comprising a foamwhich process comprises subjecting at least a part of said elastic layerto permanent compressional deformation by heating compression. It isalso desirable in this case that the cells in the elastic layer be madeto outnumber the cells in said elastic layer prior to the heatingcompression by heating compressing said elastic layer. It is desirableas the case may be, to heat and compress the elastic layer so that thesurface of said elastic layer is molten to form a skin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a shematic illustration for the explanation of a process forproducing a paper feed roller relating to the present invention.

FIG. 2 is a partially cross-sectional side view showing the paper feedroller relating to the present invention.

FIG. 3 is a perspective view showing a conventional paper feed roller.

FIG. 4 is a schematic illustration showing one example of process forproducing a paper feed roller according to the present invention.

FIG. 5 is a schematic cross-sectional view showing one example of paperfeed roller according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

It is necessary in the roller of the present invention only that atleast a part of an elastic layer be subjected to permanent compressionaldeformation by heating compression. It is desirable in particular, thatthe cells in the elastic layer be made to outnumber the cells in saidelastic layer prior to the heating compression by heating compressingsaid elastic layer. Specifically, it is desirable that the number ofcells in the elastic layer subjected to permanent compressionaldeformation be selected in the range of 1.05 to 5.00 times, especially1.05 to 3.00 times the number of cells therein prior to the heatingcompression. The above factor, when exceeding 5.00, results in a highcompression ratio and a high hardness of the roller as a whole, therebysometimes failing to obtain the objective roller. By the term "thenumber of cells in the elastic layer subjected to permanentcompressional deformation" as mentioned herein is meant the number ofcells obtained by measuring the number of cells from the surface of theelastic layer to a depth of 1 mm therefrom irrespective of the outsidediameter of the roller.

The surfacial state of the roller can be suitably varied according tothe heating compressing conditions. For example, the elastic layer, whensubjected to heating compression until its permanent compressionaldeformation, partially undergoes permanent compressional deformation,which leads to high hardness. On the other hand, the elastic layer, whensubjected to heating compression until the surface thereof is molten toform a skin, can partially be formed into a skin.

Preferable materials of construction for the elastic layer of the rolleraccording to the present invention are not specifically limited, but areexemplified by a thermoplastic foam such as polyethylene, polyvinylchloride, polystyrene, polyvinyl alcohol, viscose rayon, ionomer andpolyurethane and a thermosetting foam made from such materials aspolyurethane, rubber, epoxy resin, phenol/urea resin, polyester resin,silicone resin and acrylic resin. Of these polyurethane foam isparticularly preferable.

The form of cells in the elastic layer may be any of closed cell andintercommunicating cell for the purpose of use, of which theintercommunicating cell is preferable because of less dimensionalvariation with temperature.

In the case where the material of construction for the elastic layer isa flexible polyurethane foam, a usable polyol as a starting materialtherefor is not specifically limited, but may be any type of polyolwhether it is hydrophobic or hydrophilic. In the case of a developerconveying roller, it is preferably polyester polyol or polyether polyolfrom the viewpoint of fusion adhesivity of a toner. Likewise, a usableisocyanate as another starting material is not specifically limited, butmay be any publicly known type.

The heating compressing conditions are not specifically limited but maybe suitably altered according to the material of the elastic layer. Inthe case of flexible polyurethane foam, for example, the heatingcompressing conditions depend upon the softening point thereof, but arepreferably 120 to 220° C. and 0.5 to 20 minutes, approximately at thetime of permanent compressional deformation. By the treatment under suchconditions, the foam containing so-called cell is subjected to permanentcompressional deformation, or a thin skin layer is formed on the surfacethereof.

It is also possible to impart various properties to the elastic layer ofthe roller. Examples of elctroconductive materials for impartingelectroconductivity thereto include electroconductive carbon such asKetjen black EC and acetylene black; carbon for rubber such as SAF(Super abrasion furnace), ISAF (Intermediate super abrasion furnace),HAF (High abrasion furnace), FEF (Fast extrusion furnace), GPF (Generalpurpose furnace), SRF (Semi-reinforcing furnace), FT (Fine thermal) andMT (Medium thermal); oxidizingly treated carbon for color (ink);thermally cracked carbon; natural graphite; artificial graphite;antimony-doped tin oxide; titanium oxide; zinc oxide; oxides of metalsuch as nickel, copper, silver and germanium; and electroconductivepolymer such as polyaniline, polypyrrole and polyacetylene. Of these,the electroconductive material which is inexpensive and easy to controlelectroconductivity with a small amount is a carbon black. Theelectroconductive material is suitably used in a blending amount in therange of usually 0.5 to 50 parts by weight, especially 1 to 30 parts byweight based on 100 parts by weight of the elastic layer material.

In addition, examples of ionically electroconductive substances includeinorganic ionically electroconductive substance such as sodiumperchlorate, lithium perchlorate, calcium perchlorate and lithiumchloride; and organic ionically elctroconductive substance or chargetransfer complex such as perchlorates, sulfates, ethosulfates,methylsulfates, phosphates, borofluorides, acetates, etc. each ofquaternary ammonium that are exemplified bytridecylmethyldihydroxyethylammonium perchlorate,lauryltrimethylammonium perchlorate, modified aliphaticdimethylethylammonium ethosulfate,N,N-bis(2-hydroxyethyl)-N-(3'-dodecyloxy-2'-hydroxypropyl)methylammoniumethosulfate, 3-laurylamidepropyl-trimethylammonium methylsulfate,stearylamidepropyldimethyl-hydroxyethylammonium dihydrogenephosphate,tetrabutylammonium borofluoride, stearylammonium acetate andlaurylammonium acetate. The above-mentioned electroconductive materialis suitably used in a blending amount in the range of usually 0.0001 to50 parts by weight based on 100 parts by weight of the elastic layermaterial.

The material of construction for the shaft of the roller according tothe present invention is not specifically limited, but is exemplified bya metal and resin. A resin shaft may be imparted withelectroconductivity according to its purpose of use. Moreover, thesurfaces of the elastic layer for the roller of the present inventionmay be imparted with a coating, and in this case, the coating may beimparted, as necessary, with electroconductivity by adding thereto theabove-exemplified electroconductive material.

In the process for producing a roller according to the present inventionthere are available various methods for heating compressing the elasticlayer without specific limitation, which methods are exemplified by (1)a method in which a heated mold is pushed and pressed against the rollerequipped with an elastic layer; (2) a method in which a mold is pushedand pressed against the roller equipped with an elastic layer, followedby heating the mold; and (3) a method in which the roller equipped withan elastic layer is press fitted into a cylindrical member, at least apart of said elastic layer is compressed and thereafter said cylindricalmember is heated.

In the following, some description will be given, by way of an example,of the process for producing a paper feed roller relating to the presentinvention.

FIG. 1 is a shcematic illustration for the explanation of a process forproducing a paper feed roller relating to the present invention and FIG.2 is a partially cross-sectional side view showing the paper feed rollerobtained by the aforesaid process, wherein symbol 1 is a paper feedroller, symbol 2 is a shaft, symbols 3, 3₁ and 3₂ are each an elasticlayer and symblos 4₁ and 4₂ are each a mold.

In a first step (FIG. 1 (a)), a shaft 2 is covered with an elastic layeron the outer periphery thereof to constitute a base body 1₀ of the paperfeed roller. In this example, the elastic layer 3 is made of a flexiblepolyurethane foam having the number of cells of 65/inch, in which thecell membranes have been treated by an explosion method to formintercommunicating cells. An adhesive layer may be placed, if necessary,between the shaft 2 and the elastic layer 3 (not shown on the drawing).The exemplary elastic layer 3 which has been made into a cylindricalform in advance, may be replaced as the case may be, with an elasticlayer in the form of a polygon cut out from a foam block.

In a second step (FIG. 1 (b)), arbitrary portions, in the longitudinaldirection of the shaft 2, of the elastic layer 3 for the base body 1₀ ofthe paper feed roller is heat compressed with the molds 4₁, 4₂, that areequipped with protrusions 4₁₁, 4₁₂ at opposing positions. The base body1₀ of the paper feed roller is inserted between the molds and heatcompressed under the conditions of 140° C. for 5 minutes to subject theelastic layer 3 to permanent compressional deformation.

Through the above-mentioned processing steps, there is obtained thepaper feed roller 1, in which the elastic layer 3 is imparted withdepressions 4₀ which correspond to the protrusions 4₁₁, 4₁₂ and aresubjected to permanent compressional deformation. The number of cells onand around the surface of the depressions 4₀ of the elastic layer 3 forthe paper feed roller after heating compression is about twice thenumber of cells before heating compression. The resultant deformation isnon-restorable.

It is also possible to subject the surface of the elastic layer 3 forthe paper feed roller in addition to the depression 4₀, to permanentcompressional deformation depending upon the compressing conditions andfurther to constitute, on said surface, a thin layer almost free fromcells.

The mold material is not specifically limited, but is preferably a metalhaving a high thermal-conductivity such as aluminium, copper and iron.It is also possible to coat the inside surface thereof with afluororesin or the like to facilitate the roller to be press fittedtherein.

The method for heating compressing is not specifically limited to theabove-exemplified method by the use of molds, but may be adopted for usefrom the publicly known methods. It is possible to cause permanentcompressional deformation, for example, by forming protrusions on a flatplate, inserting the base body 1₀ for the paper feed rollertherebetween, and relatively rotating the base body 1₀ so as to be incontact with the flat plate.

As another available method, such a paper feed roller can be produced bywinding a spiral band around the base body 1₀ for the paper feed rollerand heating said band.

The above-mentioned methods are not limited to the production of a paperfeed roller, but can be applied to the production of various rollers forother purpose of use.

Subsequently, some description will be given, by way of an example, ofthe process for producing a developer conveying roller relating to thepresent invention.

Firstly, FIG. 4 (a) illustrates a roller 11, in which a shaft 12 iscovered in advance, with an elastic layer 13 on the outer peripherythereof. An adhesive layer may be placed, if necessary, between theshaft 12 and the elastic layer 13 (not shown on the drawing). Theexemplary elastic layer 13 which has been made into a roller form inadvance, may be replaced, as the case may be, with an elastic layer inthe form of a polygon cut out from a foam block.

FIG. 4 (b) illustrates the step of press fitting the roller 11 into acylindrical member 14 the inside diameter of which is smaller than theoutside diameter of said roller to compress the elastic layer. In thiscase, the cylindrical member is not specifically limited, but isexemplified by a pipe made of a metal and/or a resin, preferably a metalhaving a high thermal-conductivity such as alluminum, copper and iron,because as described hereinafter, the elastic layer is thermallycompressed by the shaft 12 and the cylindrical member 14 both beingheated. It is also possible to coat the inside surface of thecylindrical member 14 with a fluororesin or the like to facilitate theroller to be press fitted therein.

The inside diameter of the cylindrical member 14 is not specificallylimited but may be suitably varied by the extent that the insertedelastic layer is to be compressed in view of the hardness, etc. of theobjective roller. It is preferable to set the thickness of thecompressed elastic layer to about 50 to 95% based on 100% of theoriginal maximum thickness thereof.

The method for press fitting the roller into the cylindrical member isnot specifically limited, but may be adopted from publicly knownmethods.

FIG. 4 (c) illustrates the step of heating the outer periphery of theroller 11 in a state that it is press fitted into the cylindrical member14 in FIG. 4 (b). The method for heating is not specifically limited,but may be adopted from publicly known methods.

The heating temperature is not specifically limited, but may be suitablyvaried according to the material of construction for the foam to beused. It is preferably in the range of 150 to 250° C. in the case ofpolyurethane foam.

FIG. 4 (d) illustrates the final step of taking out the roller 11' fromthe cylindrical member 14 after the completion of heating in FIG. 4 (c).

In the following, an explanation will be given of the roller 11' whichis obtained through the series of the foregoing steps.

FIG. 5 is a cross-sectional view taken on line A--A of FIG. 4 (d), andpoints out that the cells in the foam is in the form of being compressedin the radial direction of the roller, and also that the cells on andaround the surface of the elastic layer outnumber the cells inside saidlayer. The radial direction as mentioned herein is the directionindicated by the arrow in FIG. 5.

The characteristics of the resultant roller 11' are as follows:

Hardness (Ascar C scale); 10 to 70 deg.

Number of cells; number of cells on and around the surface of theelastic layer being 1.05 to 3.00 times the number of cells inside saidlayer.

In the following, the above-mentioned developer conveying roller will bedescribed in more detail with reference to a working example.

EXAMPLE

There was prepared a roller having a shaft with a length of 250 mm and adiameter of 6 mm, the outer periphery of which was covered with anelastic layer having a length of 210 mm, a thicknes of 6 mm, made ofpolyurethane foam of an ester-based polyol with a hardness of 15 deg. onAscar C scale and 50 numbers of cells/inch.

The resultant roller was press fitted into the hollow part of a pipemade of aluminum with a length of 250 mm and an inside diameter of 15.5mm, heated at 185° C. for 30 minutes by means of a heating furnace andallowed to cool at room temperature to afford a roller having an outsidediameter of 15 mm. The heat treated roller thus obtained had an Ascar Cscale hardness of 16 deg., the number of cells on and around the surfaceof 150/inch and the number of cells inside the elastic layer of 60/inch.

Subsequently in order to evaluate the performance of the roller as adeveloper conveying roller, an evaluation was made of the roller byincorporating it in an image forming apparatus as a commercial machinefor the production of 2000 numbers of printed sheets in a developingapparatus. As a result, it was confirmed that the developing apparatuswas free from any undesirable foreign matter such as foam even after2000 numbers of production, and also that the apparatus had surely beenfed with a sufficient amount of the developer conveyed through theroller.

The roller having the specific constitution as described hereinbeforeand the process for prodcuing the same according to the presentinvention, facilitate the production of the roller in an economicallyadvantageous manner as compared with conventional rollers. Needless tosay, the roller according to the present invention is applicable notonly to a paper feed roller but also to a wide variety of rollers.

Owing to the specific shape of the cells being compressed in the radialdirection of the roller, smoothness and low hardness are maintained allover the elastic layer of the roller. Also, by virtue of the specificconfiguration of the cells in which the cells on and around the surfaceof the elastic layer outnumber the cells inside said layer, the surfacethereof is prevented from being clogged with the developer.

What is claimed is:
 1. A process for producing a roller for anelectrographic apparatus or an electrostatic recording apparatus havingan elastic layer comprising a foam, wherein at least a part of saidelastic layer is subjected to permanent compressional deformation byheating compression which is effected by pressing a heated mold againstthe roller equipped with an elastic layer or by pressing a mold againstthe roller equipped with an elastic layer, followed by heating saidmold, said elastic layer being subjected to the permanent compressionaldeformation by heating compression having a hardness of about 10 to 70deg. on Ascar C scale, and having a number of cells from a surface ofthe elastic layer to a depth of 1 mm therefrom being about 1.50 to 3.00times the number of cells in a depth of over 1 mm from the surface.
 2. Aprocess for producing a roller for an electrographic apparatus or anelectrostatic recording apparatus having an elastic layer comprising afoam, wherein at east a part of said elastic layer is subjected topermanent compressional deformation by heating compression which iseffected by press fitting a roller equipped with an elastic layer into acylindrical member, compressing at least a part of said elastic layerand subsequently heating said cylindrical member, said elastic layerbeing subjected to the permanent compressional deformation by heatingcompression having a hardness of about 10 to 70 deg. on Ascar C scale,and having a number of cells from a surface of the elastic layer to adepth of 1 mm therefrom being about 1.50 to 3.00 times the number ofcells in a depth of over 1 mm from the surface.
 3. The process forproducing a roller according to claim 2, wherein the heating compressionis effected so as to melt the surface of the elastic layer to form askin.
 4. The process for producing a roller according to claim 2,wherein the material of construction for the elastic layer ispolyurethane foam.
 5. The process for producing a roller according toclaim 2, wherein said roller is a paper feed roller or developerconveying roller.
 6. The process for producing a roller according toclaim 2, wherein heating compression is effected so that the cells inthe elastic layer are in the form of being compressed in the radialdirection of said roller.